Much current research in neurobiology is concerned with the question of how an animal's central nervous system (CNS) is able to generate nerve impulses in the sequence and with the timing which causes the contraction of muscles appropriate to each specific behavior of the animal. The purpose of the proposed research will be to investigate this problem by determining the roles of sensory input and central interneurons in producing and co-ordinating the movements of the legs of an insect during walking. The work will have three main objectives: 1) To provide a quantitative description of the output of those interneurons whose activity during walking suggests that they help regulate this behavior. This will be done by recording the electrical activity of interneurons in the CNS during walking, and measuring the frequency and timing of this activity relative to movements of individual legs and to the activity of other neurons. 2) To determine the fate of sensory input from the legs in the CNS--i.e., to find out what part of the information entering the CNS from sense organs in the legs is distributed beyond the ganglion through which it enters, and where it then goes. This will be done by stimulating specific sense organs in individual legs while recording neural activity from various places in the CNS. 3) To determine the effect which the sensory input has on the activity of the interneurons studied in the first part of the project. This will be done by studying the effect on the activity of these interneurons of destroying selected sense organs or central pathways, or by causing activity in the pathways at times they are usually silent.